/Engine/Source/Editor/UnrealEd/Public/Kismet2/BlueprintEditorUtils.h
Will not change the category for variables defined via native classes.
static void SetBlueprintVariableCategory ( [UBlueprint](API\Runtime\Engine\Engine\UBlueprint) * Blueprint, const [FName](API\Runtime\Core\UObject\FName) & VarName, const [UStruct](API\Runtime\CoreUObject\UObject\UStruct) * InLocalVarScope, const [FText](API\Runtime\Core\Internationalization\FText) & NewCategory, bool bDontRecompile )